The invention relates to a motor vehicle with a compartment intended for prolonged occupation by persons, said compartment having a heating system, which can be operated either by connection to the cooling-water circuit of the engine by means of the heat given off by the engine, or by connection to a separate heater independent of engine operation.
In motor vehicles in which persons must remain for a long period of time while the vehicle is parked, for example, trucks with sleeping cabs, road service vehicles, mail trucks and the like, the separate heater must be used to heat the vehicle in winter if the vehicle is occupied by persons. This separate heater is usually connected to the cooling-water circuit of the engine, said circuit in turn containing a heat exchanger, through which hot air, supplied by a blower, is blown into the interior of the motor vehicle. The noise generated by the blower as well as the air flow are extremely disturbing, especially at night. Moreover, the blower drive necessitates a relatively high energy consumption, which limits the operation of the separate heater when the vehicle is parked because of the limited capacity of the motor vehicle battery.
Thus, objects of the invention are to avoid these disadvantages and to allow the interior of a parked motor vehicle to be heated in a largely noiseless fashion, without a disturbing draft, and with a reduction of power consumption.
These goals are achieved according to a preferred embodiment of the invention by virtue of the fact that a heating element traversable by a liquid heat conductor is disposed in the passenger compartment, said heating element being connectable alternatively with the cooling-water circuit, with the separate heater, and with both.
While the vehicle is in operation, the flow of heated heat conductor can be fed through the heating element, so that it is already warm when the motor vehicle is parked. If the temperature in the compartment falls below a certain level, a thermostat turns on the separate heater, which heats up the heat conductor and therefore the heating element as well until the desired temperature is reached in the compartment. Since the separate heater is usually located outside the passenger compartment and a continuously operating hot air blower is not used, in contrast to conventional heating systems, heater operation is largely silent and draft-free.
Preferably, the heating element has a certain heat storage capacity. This results in a power saving since the heating element, as mentioned earlier, can be heated by the vehicle's own heater while the vehicle is operating, so that the heat is provided by the separate heater only after a considerable time has elapsed after the vehicle has been parked.
Preferably, the heating element is disposed in a duct which has a fresh air intake at the bottom and a hot air outlet at the top. To reduce the amount of space the system takes up, the heating element is advantageously made in the form of a plate heater. The duct can be delimited by an outside wall of the passenger compartment and a partition parallel thereto. In a motor vehicle with a driver's cab, including a sleeping compartment with a bunk, the plate heater and the partition are preferably disposed parallel to the rear wall of the cab. Combined with the back rest of the driver's seat, located in front of the bunk, a circular air flow can be created around the bunk, and this locally concentrated heating arrangement results in less power being used for heating.
In order to ensure forced hot air circulation in contact with the heating element, a hot air blower, which can be switched off, can be provided, said blower having a much lower power and lower rpm than the hot air blower used for vehicle heating, and therefore so quiet that it causes no disturbance. Thus, for example, an axial-flow fan can be used, characterized by especially low noise levels.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.